Typically, an annular combustion chamber for a turbomachine is formed by an inner annular wall and an outer annular wall that are interconnected at an upstream end by a transverse wall forming a chamber end wall.
The inner and outer walls are each provided with a plurality of holes and various orifices allowing the air flowing around the combustion chamber to penetrate into it.
Thus, so-called “primary” holes and “dilution” holes are formed through these walls to bring air into the inside of the combustion chamber. The air passing through the primary holes contributes to creating an air/fuel mixture which is burnt in the chamber, while the air passing through the dilution holes serves to encourage dilution of the same air/fuel mixture.
The inner and outer walls, which are generally made of metal, are subjected to the high temperatures of the gases that result from burning the air/fuel mixture. In order to cool them, additional “multiple perforation” orifices are also pierced through the walls over their entire area. These multiple perforation orifices allow the air flowing outside the chamber to penetrate into the inside of the chamber so as to form films of cooling air flowing along the walls.
In practice, it has been found that those zones of the inner and outer walls that are situated directly downstream from a primary hole or a dilution hole suffer from a level of cooling that is small, with the attendant risk of cracks forming.
In order to solve this problem, U.S. Pat. No. 6,145,319 proposes making transition holes through the zones of the walls that are situated directly downstream from each of the primary and dilution holes, these transition holes being inclined to a greater extent than the multiple perforation orifices. Given that that constitutes localized treatment, such a proposal is particularly expensive to implement and increases manufacturing time.